AVDT: Don't explicitly require no-security on MEDIA and REPORT

When AVDT L2cap channel is open, MEDIA and REPORT channel can use the
same security requirement as SIG channel

Bug: 159815595
Tag: #refactor
Test: compile & verify basic functions working
Change-Id: I61523062af8948053b0e5d67707a5f2fcb0b82d1